spool file

spool file /n./ Any file to which data is spooled to
await the next stage of processing. Especially used in
circumstances where spooling the data copes with a mismatch between
speeds in two devices or pieces of software. For example, when you
send mail under Unix, it's typically copied to a spool file to
await a transport demon's attentions. This is borderline
techspeak.